1. Field of the Invention
The present invention relates to an antenna device for generating plasma, and more particularly to an antenna device for generating inductively coupled plasma which can covers a large effective area to process a large specimen in a high, uniform density of plasma.
2. Description of the Prior Art
In order to produce a fine pattern on a substrate like a semiconductor wafer, flat panel display or the like in a technical field of fabricating a semiconductor device, plasma is generated to perform a variety of surface treatment process like dry etching process, chemical vapor deposition process, sputtering and the like. In order to reduce cost and improve throughput, the size of a semiconductor wafer and that of a substrate for a flat panel display has shown a tendency of getting larger, for instance, over 300 mm in recent years. Accordingly, a device for generating plasma to process such a large wafer or substrate also gets larger.
Therefore, there have been plasma sources to be operated by high frequency power in a diode type, microwave type or radio frequency wave type and the like. In this regard, there are problems in the diode type plasma source like a difficulty in controlling high voltage and requirement of a high level of gas pressure, so that the diode type plasma source has not been suitable for processing such a fine pattern. Even if an electron cyclotron resonance ("ECR") type plasma source is advantageous in obtaining a high density plasma under a low pressure, it is disadvantageous in achieving a uniform distribution of plasma. Such a problem gets more severe as the size of plasma increases. Furthermore, according to a helicon wave type plasma source, a kind of radio wave type plasma source called an inductively coupled type, the energy in electric and magnetic fields are combined and excited to be able to generate a high density plasma in uniform distribution. However, in case the size of plasma increases, the helicon wave type plasma source is not suitable for achieving a uniform density distribution of plasma.
A general antenna device for generating inductively coupled plasma will be briefly described with reference to FIG. 1. The device for generating plasma 10 (hereinafter referred to as plasma generating device) has a chamber 104 in which plasma is generated, wherein the chamber 104 includes a gas inlet opening 110 for supplying reactant gas, a vacuum pump 112 for keeping the internal part of the chamber in a vacuum state and a gas outlet opening 114 for exhausting reactant gas after reaction. In addition, there is a chuck 108 on which a specimen 112 like wafer, glass substrate or the like will be placed in the chamber 104. An antenna 100 connected with a high frequency power source 102 is installed on the chamber 104. An insulating plate 116 is installed between antenna 100 and chamber 104 for decreasing capacitive coupling characteristic, which helps transmission of energy from the high frequency power source 102 to plasma 118 through the inductive coupling.
The plasma generating device 100 thus constructed generates plasma in a method which will be described below. In other words, all the air filling in the internal part of the chamber 104 is discharged out with a vacuum pump 112 to get to a vacuum state at the first step. A reactant gas is infused for generating plasma through the gas inlet opening 110, and the chamber 104 is kept at a necessary level of gas pressure. Then, the high frequency power of 13.56 MHz is applied to the antenna device 100 from the high frequency power source 102.
As shown in FIGS. 2a and 2b, the conventional plasma generating device is constructed with a spiral shaped antenna 200 or a plurality of (for instance, three) divided electrode type antennas 202a, 202b and 202c. Therefore, with high frequency power, a vertical magnetic field is formed along with changes of time at a plane horizontal to the antenna 100. The magnetic field that changes in time as such forms an inductive electric field at the internal part of the chamber 104. When electrons are heated and induced to an electric field to thereby generate plasma inductively coupled with the antenna 100. As described above, electrons are collided with neighboring neutral gas particles to generate ions and radicals and the like which will be used for plasma etching and deposition processes. In addition, if power is applied to the chuck 108 from a separate high frequency power source (not shown), it is possible to adjust the energy of ions which will be applied to the specimen 106.
As shown in FIG. 2a, a number of wires to form a spiral shaped antenna 200 are connected in series, keeping flow of current constant in each wire. In this case, it is difficult to control distribution of inductive electric fields, and ions and electrons are lost at the internal wall of the chamber 104. Therefore, a high density of plasma is formed at the central part of the plasma 118, but a low density of plasma is formed at the part close to the internal wall of the chamber 104. As a result, it is extremely difficult to achieve uniformity in the density distribution of the plasma 118.
Furthermore, as all the wires of the antenna 200 are connected in series, there may be a great voltage drop which may increase the influence of a capacitive coupling characteristic with the plasma 118. As a result, the electrical efficiency of the antenna 200 decreases and it is difficult to keep uniformity in the density distribution of plasma.
Next, as shown in FIG. 2a, in the antenna constructed with three separate electrodes respectively connected with three different phases of high frequency power sources 204a, 204b and 204c, the density of plasma is generally high, but the density of plasma decreases at a part close to the center of the chamber 104. It is also difficult to ensure the uniformity in the density distribution of plasma, and it is more difficult to treat a large size of a specimen. In addition, application of separately operated power results in increase in cost because an independent impedance matching circuit should be used for separate electrodes to achieve an impedance matching state for efficient uses of power.